Re: [PATCH] mm, memory_hotplug: teach has_unmovable_pages about of LRU migrateable pages

Baoquan He
2018-11-05T09:45:15Z

On 11/05/18 at 10:28am, Michal Hocko wrote:
> On Mon 05-11-18 10:14:07, Michal Hocko wrote:
> > Maybe we can add a retry for movable zone pages.
>
> Or something like this. Ugly as hell, no question about that. I also
> have to think about this some more to convince myself this will not
> result in an endless loop under some situations.

Testing, will tell the result.

>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 48ceda313332..342d66eca0f3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7779,12 +7779,16 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> pfn = page_to_pfn(page);
> for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
> unsigned long check = pfn + iter;
> + unsigned long saved_flags;
>
> if (!pfn_valid_within(check))
> continue;
>
> page = pfn_to_page(check);
>
> +retry:
> + saved_flags = READ_ONCE(page->flags);
> +
> if (PageReserved(page))
> goto unmovable;
>
> @@ -7840,6 +7844,13 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> page->mapping->a_ops->migratepage)
> continue;
>
> + /*
> + * We might race with the allocation of the page so retry
> + * if flags have changed.
> + */
> + if (saved_flags != READ_ONCE(page->flags))
> + goto retry;
> +
> /*
> * If there are RECLAIMABLE pages, we need to check
> * it. But now, memory offline itself doesn't call
> --
> Michal Hocko
> SUSE Labs